1. Field of the Invention
This invention relates to an optical device for use in an optical amplifier for optical communication and so on.
2. Description of the Prior Art
The applicant for patent on this invention proposed an optical device available to an optical fiber amplifier or the like (Japanese Patent Application Publication No. 8-304855(A)).
The proposed optical device is provided with a prestage module and a poststage module which constitute the optical amplifier. The prestage module is assembled into a unit by incorporating collimators disposed on the incident side and the outgoing side of a signal beam, an unpolarizing beam splitter located between the collimators, a photodiode which receives a part of the signal beam from the incident-side collimator through the beam splitter, and a polarization-independent type optical isolator arranged between the beam splitter and the outgoing-side collimator. The outgoing-side collimator is connected to a rare-earth ion doped optical fiber.
The poststage module includes upper and lower collimators serving as incident-side optical terminals, and a collimator serving as an outgoing-side optical terminal. In the vicinity of the outgoing side of the upper incident-side collimator, a long-wave pass filter is disposed. A polarization-independent type optical isolator is disposed between the long-wave pass filter and the outgoing-side collimator in the poststage module, and a beam splitter is disposed between the optical isolator and the outgoing-side collimator.
To materialize miniaturization and elevation of the performance of the optical amplifier which is in increasing demand in recent years, there has been a need for various optical passive devices integrated effectively.
However, the conventional optical passive device, which generally incorporates lots of collimators and other component parts, has its limits in being diminished in size, and should be improved in structure to reduce its packaging area.